I. The Complement System
The complement system acts in conjunction with other immunological systems of the body to defend against intrusion of cellular and viral pathogens. There are at least 25 complement proteins, which are found as a complex collection of plasma proteins and membrane cofactors. The plasma proteins (which are also found in most other body fluids, such as lymph, bone marrow, synovial fluid, and cerebrospinal fluid) make up about 10% of the globulins in vertebrate serum. Complement components achieve their immune defensive functions by interacting in a series of intricate but precise enzymatic cleavage and membrane binding events. The resulting complement cascade leads to the production of products with opsonic, immunoregulatory, and lytic functions.
The complement cascade progresses via the classical pathway or the alternative pathway. These pathways share many components, and, while they differ in their early steps, both converge and share the same terminal complement components responsible for the destruction of target cells and viruses.
The classical complement pathway is typically initiated by antibody recognition of and binding to an antigenic site on a target cell. This surface bound antibody subsequently reacts with the first component of complement, C1. The C1 thus bound undergoes a set of autocatalytic reactions that result in, inter alia, the induction of C1 proteolytic activity acting on complement components C2 and C4.
This activated C1 cleaves C2 and C4 into C2a, C2b, C4a, and C4b. The function of C2b is poorly understood. C2a and C4b combine to form the C4b,2a complex, which is an active protease known as classical C3 convertase. C4b,2a acts to cleave C3 into C3a and C3b. C3a and C4a are both relatively weak anaphylatoxins that may induce degranulation of mast cells, resulting in the release of histamine and other mediators of inflammation.
C3b has multiple functions. As opsonin, it binds to bacteria, viruses and other cells and particles and tags them for removal from the circulation. C3b can also form a complex with C4b,C2a to produce C4b,2a,3b, or classical C5 convertase, which cleaves C5 into C5a (another anaphylatoxin), and C5b. Alternative C5 convertase is C3b, Bb, C3b and performs the same function. C5b combines with C6 yielding C5b,6, and this complex combines with C7 to form the ternary complex C5b,6,7. The C5b,6,7 complex binds C8 at the surface of a cell membrane. Upon binding of C9, the complete membrane attack complex (MAC) is formed (C5b-9) which mediates the lysis of foreign cells, microorganisms, and viruses.
Further discussions of the classical complement pathway, as well as a detailed description of the alternative pathway of complement activation, can be found in numerous publications including, for example, Roitt, et al., 1988, and Muller-Eberhard, 1988.
II. Joint Inflammation
A variety of common medical disorders have as a common element the inflammation of the patient's joints. In the United States alone, millions of patients suffer from such joint inflammation. Afflicted individuals are frequently disabled, and the costs of medical care for patients suffering from such disorders are significant. While numerous means are available for treatment of joint inflammation, and new treatments continue to become available, none of these is as safe and effective as could be desired, and there has thus been a long felt need for new approaches and better methods to control joint inflammation.
Clinically, joint inflammation is associated with joint stiffness, pain, weakness, and sometimes joint fatigue. Uniformly, the joint is tender and swollen, and often erythematous. Diagnosis of the inflammatory nature of the joint disease is frequently based upon this typical clinical presentation as well as upon radiographic examination and aspiration and examination of synovial joint fluid. Examination of joint fluid of an inflamed joint generally reveals elevation of various markers of inflammation, such as, leukocytes (including neutrophils), antibodies, cytokines, cell adhesion molecules, and complement activation products (De Clerck et al., 1989; Heinz et al., 1989; Moffat et al., 1989; Peake et al., 1989; Brodeur et al., 1991; Firestein et al., 1991; Matsubara et al., 1991; Olsen et al., 1991; Oleesky et al., 1991; Jose et al., 1990; Zvaifler, 1968; Zvaifler, 1969a; Zvaifler, 1969b; Zvaifler, 1974; Ward and Zvaifler, 1971; Ward, 1975; Moxley and Ruddy, 1985; Mollnes et al., 1986; Auda et al., 1990; Olmez et al., 1991; Kahle et al., 1992; Koch et al., 1994; Thorbecke et al., 1992; Saura et al., 1992; Feldman et al., 1990; Feldman et al., 1991; Fong et al., 1994; Harigi et al., 1993; Morgan et al., 1988; Shingu et al., 1994; Abbink et al., 1992; and Corvetta et al., 1992). Radiographic examination of affected joints generally reveals soft tissue swelling and/or erosive changes.
Joint inflammation is associated with a group of diseases that are referred to medically as arthridities (types of arthritis). The term “arthritis” is used medically to generally describe diseases of the joints. The term, however, is also used to describe certain medical conditions, of which rheumatoid arthritis (RA) is the primary example, that consist of a multiplicity of different pathologic manifestations, including, but by no means limited to, joint disease.
Discussions of arthritis may thus include diseases such as RA, where joint disorders are only one facet of the varied pathologies associated with the disease. The present invention is directed specifically to the joint disorder aspects of these diseases. The methods of the invention, however, may also have beneficial effects on non-joint-associated pathologies. For example, use of the methods of the invention to treat established joint inflammation associated with RA, psoriasis, lupus, and other disorders may also provide therapeutic benefits impacting on some of the other pathologic manifestations of these multifaceted disease states, such as vascular inflammation and nephritis (see, for example, Wurzner, et al., Complement Inflamm. 8:328-340, 1991; U.S. application Ser. No. 08/217,391 filed on Mar. 23, 1994, abandoned; U.S. application Ser. No. 08/236,208 filed on May 2, 1994, now U.S. Pat. No. 6.074,642; and Sims, et al., U.S. Pat. No. 5,135,916).
It should be noted that the present invention is not concerned with all types of joint disorders, but only those involving inflammation. Thus, for example, the invention is applicable to the treatment of late-stage osteoarthritis (OA), which is an inflammatory joint disease, but generally not to early stage OA, which does not typically have a significant inflammatory component.
Detailed discussions of the arthridities can be found in numerous medical texts, including Arnett, 1992. Cecil Textbook of Medicine, Wyngaarden et al. (eds.), W. B. Saunders Company, Philadelphia, Chapter 258, pp. 1508-1515; Lipsky, 1994. Harrison's Principles of Internal Medicine, 13th Ed., Isselbacher et al. (eds), McGraw-Hill, Inc., New York, Chapter 285, pp. 1648-1655; and McCarty and Koopman, 1993. Arthritis and Allied Conditions, 12th Ed. Lea and Febiger, Philadelphia. As discussed in detail in these and other texts, and reviewed below, joint inflammation is associated with numerous local and systemic disease processes.
Factors Associated with Joint Inflammation
Joint inflammation is a complex process involving, among other things, activation of both cellular and humoral immune responses.
Cellular immune responses include infiltration by white blood cells, predominantly neutrophils (also referred to as polymorphonuclear cells or PMNs). Mononuclear white blood cell infiltrates are also common in many inflamed joints. Infiltrating mononuclear cells, including T lymphocytes (as well as cells resident within the joint such as synovial cells, fibroblasts, and endothelial cells) are activated and contribute to the production of multiple inflammatory cytokines including TNF-α, IL-1, IFN-γ, IL-2, IL-6, IL-8, GM-CSF, PDGF and FGF, these latter two being capable of stimulating synovial cell proliferation.
All of these cytokines are thought to play a role in inducing the production of numerous other inflammatory factors as well as various other mediators of tissue degradation. These factors and mediators of degradation include products of arachidonic acid metabolism (that are active in various intracellular signal transduction pathways), reactive oxygen intermediates, and degradative enzymes such as collagenase, stromelysin, and other neutral proteases, all of which can further contribute to the inflammatory response and to tissue destruction.
Cellular infiltration into the synovium is enhanced by the upregulation of cell adhesion molecules such as selecting, LFA-3, and members of the ICAM family of Ig-like cell adhesion molecules on cells within the joint. These adhesion molecules promote the infiltration of activated white blood cells into the affected joint by stimulating leukocyte (including lymphocyte) adhesion, migration, and activation.
The humoral immune system also contributes to joint inflammation. Antibodies are produced within inflamed joints in such diseases as RA, JRA and OA (see below) and generate localized immune complexes that can activate the complement system. As discussed above in greater detail, activated complement components can have cytolytic, cell activating, anaphylatoxic, and chemotactic effects.
These multifactorial inflammatory responses lead to cartilage destruction and bone erosion that ultimately result in the joint deformity seen in patients with chronic joint inflammation.
In view of the complex nature of joint inflammation, a variety of theories, many of which are conflicting, have been proposed in the art to explain the relative importance of the various factors involved. Notwithstanding extensive work, there remains a basic controversy in the art as to the relative roles of the cellular and humoral immune systems in joint inflammation, including what role complement plays in such inflammation. See, for example, Andersson and Holmdahl, 1990; Brahn and Trentham, 1989; Chiocchia et al., 1990; Chiocchia et al., 1991; Durie et al., 1993; Goldschmidt et al., 1990; Goldschmidt and Holmdahl, 1991; Holmdahl et al., 1985; Holmdahl et al., 1989; Holmdahl et al., 1990; Hom et al., 1988; Hom et al., 1992; Hom et al., 1993; Mori et al., 1992; Myers et al., 1989A; Nakajima et al., 1993; Osman et al., 1993; Peterman et al., 1993; Seki et al., 1988; Seki et al., 1992; Terato et al., 1992; Watson et al., 1987; and, in particular, the following reports relating to the complement system and/or the relative roles of T cells and complement components in joint inflammation: Andersson et al., 1991; Andersson et al., 1992; Banerjee et al., 1988B; Banerjee et al., 1989; David, 1992; Fava et al., 1993; Haqqi et al., 1989; Kakimoto et al., 1988; Maeurer et al., 1992; Morgan et al., 1981; Moxley and Ruddy, 1985; Reife et al., 1991; Spinella et al., 1991; Spinella and Stuart, 1992; van Lent et al., 1992; Watson et al., 1987; Watson and Townes, 1985; and Williams et al., 1992A. To date, these wide ranging studies have not led to effective treatments for established joint inflammation based on modulation of the complement system and, in particular, based on the use of C5 blockers.
The studies of the prophylactic effects of C5 blockers reported below in Example 2 were designed to determine if C5 was an appropriate and effective target for pharmacological modulation of the humoral immune system in order to prevent joint inflammation. The surprising effectiveness of C5 blockers in preventing onset of joint inflammation led to the design and execution of the studies reported in Example 1 in which C5 blockers were used to treat established inflammation. At the outset of these experiments, it was anticipated that such treatment would have little measurable effect upon established joint inflammation, as it was supposed that C5 was more important early in the disease process when the chemotactic activity of C5a would trigger the infiltration of inflammatory cells. It was further supposed that the involvement of T cells in established disease would continue to provide significant inflammatory stimuli even in the absence of C5 activity. As shown by the results of Example 1 this expectation was incorrect in that C5 blockers were found to be surprisingly effective in arresting and/or reducing the inflammation of joints which were already inflamed, while at the same time inhibiting the spread of inflammation to unaffected joints.
Diseases Commonly Associated with Joint Inflammation
Rheumatoid arthritis (RA) and juvenile onset rheumatoid arthritis (JRA) are chronic multisystem diseases of unknown cause. RA affects approximately 1% of the population, with women affected three times more commonly than men. The onset is most frequent during the fourth and fifth decades of life. RA and JRA are systemic diseases with numerous pathologic manifestations in addition to their joint inflammatory aspects. In RA, these manifestations include RA vasculitis (inflammation of the blood vessels), which can affect nearly any organ system and can cause numerous pathologic sequelae including polyneuropathy, cutaneous ulceration, and visceral infarction. Pleuropulmonary manifestations include pleuritis, interstitial fibrosis, pleuropulmonary nodules, pneumonitis, and arteritis. Other manifestations include the development of inflammatory rheumatoid nodules on a variety of periarticular structures such as extensor surfaces, as well as on pleura and meninges. Weakness and atrophy of skeletal muscle are common.
The joint inflammation aspects of RA present as persistent inflammatory synovitis, usually involving peripheral joints in a symmetric distribution. In general, the complex intraarticular inflammatory response seen in RA is of the type described above in the general discussion of joint inflammation.
Many patients with systemic lupus erythematosis (SLE) also develop joint inflammation referred to as lupus arthritis. SLE is an autoimmune disease of unknown cause in which numerous different cells, tissues, and organs are damaged by pathogenic autoantibodies and immune complexes. Clinical manifestations of SLE are numerous and include a variety of maculopapular rashes, nephritis, cerebritis, vasculitis, hematologic abnormalities including cytopenias and coagulopathies, pericarditis, myocarditis, pleurisy, gastrointestinal symptoms, and the aforementioned joint inflammation.
Osteoarthritis (OA) represents the most common joint disease of mankind, and OA of the knee is the leading cause of chronic disability in developed countries. It is manifested by pain, stiffness, and swelling of the involved joints. Articular cartilage, responsible for the most critical mechanical functions of the joint, is the major target tissue of OA. The breakdown of articular cartilage in OA is mediated by various enzymes such as metalloproteinases, plasmin, and cathepsin, which are in turn stimulated by various factors that can also act as inflammatory mediators. These factors include cytokines such as interleukin-1, which is known to activate the pathogenic cartilage and synovial proteases.
The identification of above normal levels of immunoglobulin in cartilage in generalized OA and the demonstration of type II collagen-specific antibodies in some OA patients provide evidence of a role for immune activation in this disease state (see, for example, Jasin, 1989). The observation that OA rarely remains monoarticular also suggests that this disease is a systemic disorder of articular cartilage. Synovial inflammation becomes more frequent as the disease progresses. In fact, in late stage OA, histologic evidence of synovial inflammation may be as marked as that in the synovium of patients with RA-associated joint inflammation.
Psoriatic arthritis is a chronic inflammatory joint disorder that affects 5 to 8% of people with psoriasis. A significant percentage of these individuals (one-fourth) develop progressive destructive disease. Twenty-five percent of psoriasis patients with joint inflammation develop symmetric joint inflammation resembling the joint inflammation manifestations of RA, and over half of these go on to develop varying degrees of joint destruction.
Other Diseases Associated with Joint Inflammation
A variety of other systemic illnesses have joint inflammation as a prominent feature of the clinical presentation.
Peripheral joint inflammation occurs in as many as one-fifth of patients with inflammatory bowel disease. The joint inflammation is acute, associated with flare-ups of the bowel disease, and is manifested by swollen, erythematous, warm, and painful joints. Synovial fluids of sufferers have an acute inflammatory exudate of mostly neutrophils, and radiographs demonstrate soft tissue swelling and effusions.
The synovitis that accompanies hepatitis B resembles serum sickness, with abrupt onset of fever and articular inflammation. There is generally a symmetric inflammation of joints including the knee, shoulder, wrist, ankles, elbow, and the joints of the hands. Immune complexes containing hepatitis B antigens are present in serum and synovium, lending support to the concept that the synovitis is immunologically mediated. Other viral diseases associated with joint inflammation include rubella, human immunodeficiency virus infection, coxsackieviral, and adenoviral infections.
An immune complex mediated joint inflammation is also associated with intestinal bypass surgery, and joint inflammation is a prominent manifestation of Whipple's disease, or intestinal lipodystrophy, where fever, edema, serositis, lymphadenopathy, uveitis, and cerebral inflammation are associated findings. Furthermore, potentially immunologically-related joint inflammation is an associated sequelum of infectious endocarditis and certain spirochetal infections, most notably infection with Borrelia burgdorferi, the causative organism of Lyme disease.
Primary Sjögrens syndrome is a chronic, slowly progressive autoimmune disease characterized by lymphocytic infiltration of the exocrine glands resulting in xerostomia and dry eyes. One-third of patients present with systemic manifestations, including vasculitis, nephritis, mononeuritis multiplex, and, most commonly, joint inflammation.
Ankylosing spondylitis (AS) is an inflammatory disorder of unknown cause that affects primarily the axial skeleton, but peripheral joints are also affected. Its incidence correlates with the HLA-B27 histocompatibility haplotype, and immune-mediated mechanisms are further implicated by elevated serum levels of IgA and an inflammatory joint histology with similar characteristics to those seen in the joint inflammation aspects of RA. Thus, synovial fluid from inflammatory peripheral joints in AS is not distinctly different from that of other inflammatory joint diseases.
Reactive arthritis (ReA) refers to acute nonpurulent joint inflammation complicating an infection elsewhere in the body. Reactive arthritis is believed to be immunologically mediated. Included in this category is the constellation of clinical findings often referred to as Reiter's syndrome or Reiter's disease. In addition to joint inflammation, this syndrome affects the skin, eyes, mucous membranes, and less commonly the heart, lungs, and nervous system. Reiter's syndrome may follow enteric infections with any of several Shigella, Salmonella, Yersinia, and Campylobacter species, and genital infections with Chlamydia trachomatous. The histology of joints affected by this syndrome is similar to that seen in other types of joint inflammation. The joint inflammation is usually quite painful, and tense joint effusions are not uncommon, especially in the knee. The joint inflammation is usually asymmetric and additive, with involvement of new joints occurring over a period of a few days to several weeks.
III. Current Therapies
Current therapies for the various types of joint inflammation discussed above include the administration of anti-inflammatory drugs such as non-steroidal drugs, including aspirin, and non-specific immunosuppressive drugs, such as gold compounds, corticosteroids, penicillamine, hydroxychloroquine, methotrexate, azathioprine, alkylating agents such as cyclophosphamide, and sulfasalazine. Administration of each of these agents is sometimes associated with severe side effects and toxicities. Patients receiving certain of these treatments are also exposed to the dangers of opportunistic infection and increased risk of neoplasia associated with generalized immunosuppression. In addition to the medical texts cited above, discussions of drugs used to treat established joint inflammation can be found in Goodman and Gilman's The Pharmacological Basis of Therapeutics 18th Ed., Gilman et al. (eds.) 1990, Pergamon Press, Inc., New York, Chapter 26, pp. 638-681; Physician's Desk Reference 47th Ed., 1993, Medical Economics Co., Inc., Montvale, N.J.; The United States Pharmacopeia 22nd Ed., 1989, Mack Printing Co., Easton, Pa.; Drug Evaluations Annual 1991, 1990, American Medical Association, Milwaukee, Wis.; and Cash and Klippel, 1994, N. Eng. J. Med. 330, pp. 1368-1375.
In addition to pharmacologic treatments, relief of the symptoms of joint inflammation is sometimes achieved with warm or cold soaks. Surgical intervention using tendon release procedures and/or joint replacement procedures is frequently the last resort for treatment of chronic joint inflammation. Such orthopedic surgery is associated with increased infection and prostheses have limited life spans.
New therapeutic approaches currently being developed include attempts to address various elements of the cellular immune response contributing to the inflammatory cascade present in inflamed joints. These approaches include the administration of therapeutic preparations including anti-T cell and/or anti-cytokine agents (see, for example, Banerjee et al., 1988A; Cannon et al., 1990; Chiocchia et al., 1991; Elliot et al., 1993; Fava et al., 1993; Fujimori et al., 1993; Griswold et al., 1988; Hom et al., 1988; Hom et al., 1991; Hom et al., 1993; Inoue et al., 1993; Kakimoto et al., 1992; Kleinau et al., 1989; Myers et al., 1989b; Myers et al., 1993; Nagler-Anderson et al., 1986; Nishikaku and Koga, 1993; Peterman et al., 1993; Piguet et al., 1992; Smith et al., 1990; Spannaus-Martin et al., 1990; Thompson et al., 1988; Trentham et al., 1993; Williams et al., 1992b; Williams et al., 1994; and Wolos et al., 1993).